In a baseband module of a radio base station apparatus, for reasons of achieving a redundant configuration and a load distribution configuration to improve reliability, there are cases in which a plurality of functional modules having the same function operate independently with respect to a single cell.
Among these functional modules, a radio scheduling module is a functional module that appropriately distributes resources in a cell to users. Consequently, when there are a plurality of radio scheduling modules available for a single cell, it is preferable that radio resources in the cell be divided and allocated to each radio scheduling module such that no competition of resources occurs even when the respective radio scheduling modules concurrently operate.
In many cases, radio resources are managed by being divided in a frequency direction and in a time direction. For example, it is conceivable that, by allocating radio resources to two radio scheduling modules by time division or frequency division, the radio scheduling modules can operate independently. In particular, the allocation of resources by frequency division, as compared with that by time division, has merits such as small delay, and less restriction for resource allocation.
Meanwhile, a physical downlink control channel (PDCCH), which is a downlink control channel in Long Term Evolution (LTE), is allocated with the logical aggregation of resources referred to as a control channel element (CCE). The resource used for the transmission of the PDCCH is expressed by two parameters, namely the physical number of resources in the CCE referred to as an aggregation level and an index that indicates the position of the resource provided for each aggregation level.
The allocation of resources to user equipment (UE) in the PDCCH is limited by a search area that is calculated by a pseudorandom number for each sub-frame with an index value for identifying the UE within the cell uniquely set for each UE as a seed. The index value for identifying the UE within the cell is referred to as cell radio network temporary identification (C-RNTI), for example.
As a conventional method for determining the amount of resources (for example, the number of CCEs) for a PDCCH allocated to the UE, a method has been developed for determining the aggregation level indicative of how many CCEs in a row are to be allocated to the PDCCH on the basis of a channel quality indicator (CQI) notified from the UE.
Patent Document 1: Japanese Laid-open Patent Publication No. 2010-114781
Non-patent Document 1: 3GPP, TS36.213, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Layer Procedures”.
The range of PDCCH resources usable by the UE is determined at random by a pseudorandom number for each sub-frame, and a radio scheduling module selects a PDCCH resource (one or more CCEs) to allocate for the UE out of them. Consequently, when UEs are divided into two groups, it is difficult for two radio scheduling modules to independently allocate resources such that no collision will occur between them. As in the foregoing, it has been difficult for the two radio scheduling modules, which perform the allocation of a PDCCH resource, to operate independently of each other.
Furthermore, as in the foregoing, it is conceivable that the division of resources by frequency division is, as compared with the division of resources by time division, advantageous in terms of delay, and flexibility in a ratio of resource division. However, it is difficult to divide the PDCCH, for which the usable radio resources for each UE are determined by a pseudorandom number, into a plurality of areas.